Fracturing methods commonly involve a technique of starting at the well bottom or isolating a portion of the well that is not to be perforated and fractured with a plug. The first zone is then perforated and fractured and then another plug is placed above the recently perforated zone and the process is repeated in a bottom up direction until all the zones are perforated and fractured. At the end of that process the collection of barriers are milled out. To aid the milling process the plugs can be made of non-metallic or composite materials. While this technique is workable, there was still a lot of time spent to mill out even the softer bridge plugs and remove that milling debris from the wellbore.
In the past there have been plugs used that are milled out as described in U.S. Pat. No. 7,533,721. Some are forcibly broken to open a passage such as in U.S. Pat. No. 6,026,903. Other designs created a plug with material that responded to a magnetic field as the field was applied and removed when the field was removed. This design was described in U.S. Pat. No. 6,926,089 and 6,568,470. In a multi-lateral application a plug was dissolved from within the whipstock to reopen the main bore after the lateral was completed. This is described in U.S. Pat. No. 6,145,593. Barriers that assist in extending telescoping passages and then are removed for access to fracture the formation are described in U.S. Pat. No. 5,425,424. Longitudinally extending radially expanded packers to get them to release is shown in U.S. Pat. No. 7,661,470.
In a variation of the above designs US Publication 2013/0000914 discusses a thin wall mandrel that is then expanded to enlarge the passage through the mandrel as a way of increasing production after sequential fracturing is over. While this design addressed the need for a larger bore diameter for subsequent production, the design still had issues with collapse resistance when the packer was set and the pressures used in fracturing were applied to the annular space causing an excessive compressive collapse force on the frack packer mandrel.
More recently a design to temporarily support a shear component in a shear plane has been described by William Hered and Jason Barnard in an application called Reinforced Shear Components and Methods of Using Same. Here a disc was interposed in the shear plane and retained in position against a bias force. At a predetermined time the bias force was allowed to move the disc out of the shear plane so that the structure was weakened in the shear plane and the desired failure could occur in the shear plane to release two members to move relatively.
The present design seeks to address the need for compressive strength against external pressures that would otherwise cause a collapse while at the same time addressing the later need for a larger flow diameter for subsequent production where the fracking was done and there no longer was a need to hold back against compressive collapse forces from outside the mandrel. This is accomplished without a need for expansion. A tubular insert is made of structural tubular materials preferable controlled electrolytic materials or CEM. Controlled electrolytic materials have been described in US Publication 2011/0136707 and related applications filed the same day. The related applications are incorporated by reference herein as though fully set forth. After the packer is set in tension and subjected to fracturing forces it no longer needs high collapse resistance and the CEM sleeve is removed to make a larger flow diameter for subsequent production. Although a fracturing example is used illustratively to describe how the invention operates, those skilled in the art will appreciate that other applications are envisioned where a tubular structure responds to differing pressure conditions at different times in a service life. For example in the fracking situation the anticipated tensile load for production is about 30,000 to 50,000 pounds force and for fracturing can be orders of magnitude higher. Those skilled in the art will better appreciate these and other aspects of the present invention from the detailed description and the associated drawings while recognizing that the full scope of the invention can be obtained from the appended claims.